1. Field of the Invention
The invention relates to a process for the production of multilayer structures which bear at least one metal layer. The invention further relates to multilayer products comprising at least three layers which comprise a substrate layer made of a substrate comprising specific copolycarbonates, a metal layer, and at least one other layer.
2. Description of Related Art
Because polycarbonates have high heat resistance they are used inter alia in fields where a relatively high level of thermal stress is likely to occur. Specific copolycarbonates can be used to achieve a further increase in heat resistance (an example being a copolycarbonate based on bisphenol A and bisphenol TMC (1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane)). Said polycarbonates are therefore also suitable for the production of lenses, reflectors, lamp covers, and lamp housings, etc., where these have a relatively high level of exposure to thermal stress. These applications practically always demand a relatively high level of thermal properties, for example high Vicat softening point (heat resistance) or high glass transition point combined with adequate mechanical properties.
Polycarbonates made of bisphenol A and bisphenol TMC are attainable commercially with trademark Apec® from Bayer Materialscience AG.
The application of metals to the polymer can be achieved by way of various methods, for example by vapor deposition or by sputtering. The processes are described in more detail by way of example in “Vakuumbeschichtung Bd.1 bis 5 [Vacuum coating, Vols. 1 to 5]”, H. Frey, VDI-Verlag Dusseldorf 1995 or “Oberflächen- and Dünnschicht-Technologie [Technology of surfaces and thin layers]” Part 1, R. A. Haefer, Springer Verlag 1987.
In order to achieve better metal adhesion and in order to clean the substrate surface, the substrates are normally subjected to plasma pretreatment. Plasma pretreatment can sometimes alter the surface properties of polymers. These methods are by way of example described by Friedrich et al. in Metallized plastics 5 & 6: Fundamental and applied aspects and H. Grünwald et al. in Surface and Coatings Technologiy 111 (1999) 287-296.
Further layers such as corrosion-reducing protective sizes can be applied in a PECVD (plasma enhanced chemical vapor deposition) or plasma polymerization process. Here, low-boiling-point precursors mainly based on siloxane are vaporized into a plasma and thus activated, so that they can form a film. Typical substances here are hexamethyldisiloxane (HMDSO), tetramethyldisiloxane, decamethylcyclopentasiloxane, octamethylcyclotetrasiloxane and trimethoximethylsilane.
Copolycarbonates based on cycloalkylidenediphenols are known and have been described various publications.
DE 3 903 103 A1, EP 414 083 A2, and EP 359 953 A1 describe the production and use of polycarbonates based on cycloalkylidenediphenols.
Many compositions comprising copolycarbonates with cycloalkylidenediphenols and various other polymeric components have also been described.
EP 362 646 A2 describes blends of copolycarbonates with cycloalkylidenediphenols and with rubbers.
EP 401 629 A2 describes blends with high temperature resistance made of copolycarbonates comprising cycloalkylidenebisphenols and ABS polymers.
None of said applications describes improved optical properties in metalized moldings at temperatures above 160° C. No publication describes processes for production of metalized moldings. The available prior art does not reveal any way of solving the problem described above.
U.S. Pat. No. 7,128,959 B2 describes metalized moldings. Substrate material that can be used here comprises polycarbonates polysulfones, or polyetherimides, or a mixture of these. In order to ensure good metalization, it is necessary to apply a base layer to the respective substrate prior to metalization. The problem described here cannot be solved by applying a base layer. The application of a base layer is not necessary in the case of the composition described in the present invention.
These materials must not only have good processability and good mechanical properties but must also comply with other requirements such as good surface quality in the resultant injection-molded part/extrudate, and also good metal adhesion.
Heat resistance and mechanical properties can be varied widely, depending on bisphenols used and on suitable adjustment of the molecular weight of the copolycarbonates. However, there continues to be a requirement for a further improvement in metal adhesion for certain applications. Specifically in the field of reflectors, good metal adhesion is essential.
As described above, the corresponding metalized parts must have high temperature resistance. No fall-off is permissible in either mechanical properties or optical properties, for example the quality of the metal surface. It has been found, however, that metalized moldings made of specific copolycarbonates which have Vicat softening points above 160° C., in particular above 170° C., and which comprise inter alia 1,1-bis(4-hydroxyphenyl)cyclohexane derivatives often lack adequate optical quality for specific applications at very high temperatures. Surprisingly, therefore, moldings of this type which have been pretreated and metalized under specific conditions, in particular under plasma conditions, have a tendency toward blistering under specific conditions (blistering and cracking of the coating) at high temperatures (in particular at temperatures or temperature peaks above 170° C.). This can lead to failure of the corresponding molding in the respective application. The blistering causes the metal surface to lose its uniform appearance—reflection of light is moreover adversely affected.
Surprisingly, this phenomenon occurs in particular when the abovementioned copolycarbonates comprise certain additives such as certain heat stabilizers or certain pigments such as titanium dioxide. Heat stabilizers normally serve to protect the substrate material from effects of heat, but certain heat stabilizers surprisingly achieve an opposite effect. However, titanium dioxide is used with the aim of establishing a certain color in resultant moldings and is therefore an important constituent of colored compositions. In the event that titanium dioxide is used, the amount used of titanium dioxide is from 0.10% by weight to 2.50% by weight, preferably from 0.20% by weight to 1.50% by weight and with particular preference from 0.80% by weight to 1.40% by weight, based in each case on the weight of the copolycarbonate. A result of omitting titanium dioxide and/or heat stabilizers is use of other pigments and compounds which are markedly more expensive and thus render the process less economic and/or are unstable on aging. Other colorants or pigments can be used alongside titanium dioxide, for example carbon black. An example of a color frequently desired in the field of electronics is gray (an example being what is known as “electrical gray”). Pigments of this type based on titanium dioxide are normally inert, but surprisingly the presence of these pigments leads to drastically impaired surface quality after thermal stress.
However, the phenomenon also occurs in the absence of these heat stabilizers or pigments, and the processes known hitherto from the prior art do not therefore ensure that the copolycarbonates remain defect-free at an elevated temperature.